Multirange tuner for ultra high frequency transmitters



March 23, 1948. J DODDS ET AL 2,438,474

MULTIRANGE TUNER FOR ULTRA HIGH FREQUENCY TRANSMITTERS F'iled Dec. 29, 1943 2 Shgets-Sheet 1 Hal.

1 l JOHN M. D0005,

JOHN LUDLOW, BY MM 6 INVENTORS: v

ATTORNEYS.

March 23, 1948. J, DODDS ET AL 2,438,474

- MULTIRANGE TUNER FOR ULTRA HIGH FREQUENCY TRANSMITTERS Filed Dec. 29, 1943 2 Shet-Sheet 2 INVENTORS: .JoHN M. 0 0005, 7

J0 H. LUDLO Arronmzva.

Patented Mar. 23, 1948 MULTIRAN GE TUNER FOR. ULTRA HIGH FREQUENCY TRAN SMITTERS John Mathieson Dodds, Timperley, and John Heywood Ludlow, Bowdon, England Application December 29, 1943, Serial No. 516,103

' In Great Britain May 13, 1938 13 Claims. 1

This invention relates to radio transmitters of the kind in which provision is made for changing expeditiously the wavelength of transmission by the substitution of difierent tuning inductances the one for another. Such arrangements are mostly employed in transmitters operating on relatively short wavelengths such as in the range of from 13 to 70 metres which is used for beam working wherein owing to changes in conditions of propagation an alteration of wavelength is usually necessary to be effected frequently in order to ensure reasonable continuity of service. I

In general, the wave changing arrangements comprise a number of inductances or tuned circuits mounted upon a rotating structure or turntable each inductance being provided with switch contacts so that any one of the inductances or tuned circuits can be connected to the associated power valve or valves. Such arrangement permits the change to be made in a relatively short time. Since on beam stations a separate aerial array is used for each wavelength, a selector switch has also to be operated to connect the appropriate feeder lines to the transmitter. In the use of such a rapid wave changing arrangement, having rotated the turntable to substitute one inductance or tuned circuit for another, the operator then sets the various variable tuning condensers to predetermined positions or values and causes the power to be applied, a final adjustment of the tuning condensers being usually necessary.

An object of the present invention is to provide improved wave changing arrangements whereby on the one hand to avoid or minimise certain disadvantages inherent in the prior arrangements and on the other hand to permit operation on wavelengths considerably shorter than has heretofore been possible, at reasonable efiiciency, with the known arrangements. Some of the disadvantages of the known Wave changing arrangements are as follows.

Firstly there is the delay and complication which arises from the necessity of operating an extra aerial selector switch.

Secondly as hereinbefore stated, it has not been possible to transmit on difierent wavelengths at high powers and very short wavelengths of 13 metres and lower.

Thirdly as will hereinafter appear the mechanical arrangements hereinbefore employed have made the use of simple and effective electric switch connections difficult or unsatisfactory.

Fourthly additional contacts are usually required for the high tension supply connection 2 and also for the feeder line to the aerial selector switch.

Fifthly, the arrangement is in general bulky and relatively clumsy.

Sixthly, when it is desired to alter one set of inductance coils to another set for operation on a difierent group of wavelengths, the necessary operation is lengthy and difiicult.

The present invention is only conveniently applicable with push-pull circuits, or symmetrical ,or quasi push-pull circuits wherein a condenser is substituted symmetrically for one of the two valves of a push-pull circuit. For a fuller understanding of a quasi push-pull circuit a comparison may be made between Fig. 2 or Fig. 3 and Fig. 5 of the drawings accompanying the specification of British Letters Patent No. 476,188, Fig. 5 well illustrating diagrammatically a push-pull circuit whereas Figs. 2 and 3 illustrate an arrangement of a symmetrical or quasi push-pull circuit.

In the remainder of the present specification, for the sake of brevity the invention will be described as applied to a push-pull circuit proper which is preferably, although not exclusively, similar to that illustrated by Fig. 5 of the Letters Patent just above mentioned. Moreover the valve or each valve is in accordance with British Letters Patent No. 414,753 or with British Letters Patent No. 458,702, or for operation on very short wavelengths, in accordance with British Letters Patent No. 497,359.

The arrangement according to the present invention is applicable to both what may be called parallel and series circuits, the former being usually preferable for anode circuits and the latter sometimes desirable for control grid circuits when operating on very short waves.

In the case of a parallel circuit one may consider a single inductance having connected across its terminals a parallel condenser which will usually be variable, the two joint terminals of said inductance and condenser being connected to respective electrodes of two similar condensers, the other electrodes of which are connected actually or so far as high frequency is concerned to earth. Thus the inductance terminals may be connected to the two anodes of a pair of tetrodes or other valves having screening grids which anodes constitute electrodes of the aforesaid similar condensers the other electrodes of which are the screening grids of the valves.

In the case of a series circuit one may consider two similar inductances having connected between them in series a condenser which will usually be variable, the other ends of the two inductances being connected to the similar condensers which in this case may be comprised of the control grids of the valves on the one hand and on the other hand the screening grids and cathodes of the valves.

As an example the anode-to-earth capacity may be of the order of 55 micromicrofarads and the anode swing may be 8,000 volts; whilst in the case of the series grid circuit the grid-to-earth capacity may be say 88 micromicrofarads and,

. Upon consideration of the above parallel and the control grid swing may be say 1500 volts.

series circuits it will be appreciated that the switch arms which are necessary for rapid inductance change have themselves'an inherent inductance which should be made as smallas pos= sible.

The present invention comprises a pair of push 'requiredlto be differently connected, said hinges,

switch arms and inductance contacts or jaws having a relatively large dimension in the direction parallel with the axis of the inductance loop or loops which is or are formed by said arms, hinges and contacts.

Preferably the hinges of the switch armsare connected directly to the valveterminals so as to be supported by the latter. Furthermore the several switch arm hinges are preferably arranged co-axially so that the arms can be operated in unison such as by a shaft which may be appropriately insulated.

In carrying out the invention for a parallel circuit, which is preferred for the anodes of the push-pull valves, since in this case each inductance coil, with or without parallel tuningcondensers associated therewith, is only connected 7 at its end to the valve anodes, there isrequired only one pair of switch arms. The high tension 7 4 in most cases owing to the high frequency voltages which are likely to appear across the series condenser. Each pair of inductance coils may be provided with its own series capacity and in this case a switching arrangement identical with that described for the parallel circuit may be employed. By reason however of space limitation on the shorter wavelengths it is preferred to use a single condenser fixed with relation to the valves and connected selectively between the inductances by means of a second pair of switch arms-which are conveniently disposed between the pair of switch arms which connect the terminals of the inductances to the respective valve electrodes, namely trol grids.

This arrangement is convenient furthermore in that the condenser can be readily used for-parto the terminals of the con- :allel tuning also if' required. -To this end the outsidejaws or contacts may be connected to the terminals of a single inductance by respective straps whilst the pair of inner switch arms connect across said inductance terminals a tuning condenser, V a a Regarding the feeder. connections the'preferred arrangement according to the present invention is to connect a feeder to each inductance not only in the transmitter output circuit, but also in the earlier stages thereof. Thus where anoutput and a drive stageare both provided with switching V arrangements according to the invention, ,each anode coil of the drive stage may be connected by a feeder to a corresponding grid, coil on the output stage, whilst in the anode circuit of the output stage each coil may be permanently connected to its appropriate aerial feeder.

It will be appreciated that the switching ar-.

rangement according to the invention not only may permit the elimination of the aerial selector switch heretofore employed, but permits each feeder to be correctly -lined-up for impedance up tothe output circuit. Inthe case of a separate aerial selector switch onthe other hand the. lining-up for adjusting the feeder between the switch and the transmitter so that it has the same characteristics for all wavelengths is often difiicult, especially on the shorter wavelengths.

supply may be led to the anodes through suitable chokes but it will usually be preferable to apply the high tension to the electrical centre of each inductance, For this purpose a third central switch blade may be used to connect the high tension supply selectively to the inductance coils. It is, however, preferable, at least when operating on the shorter wavelengths,

. to apply the high tension voltage to all the coils simultaneously so that the anodes are fed only through the particular cell selected by the switch arms. This feature is a subsidiaryone of the present invention.

' It will be appreciated that the required tuning condensers may be fitted to each inductance coil or alternatively a single trimming or tuning con-' denser may be connected directly between'the valve anodes, the latter arrangement being preferable for the shorter wavelengths since the switch arms themselves provide a large partof the total inductance whilst a condenser which 'shunts the coil only is relatively ineffective.

Referring now to the application of the invention to a series circuit, such circuit is useful 7 for grid tuning in cases where a parallel resonance by reason of high grid-to-earth capacity is diflicult to obtain. On the other hand the series circuit is less desirable for anode tuning,

It will be appreciated that the arrangement according to the invention permits rapid operation: particularlyas theswitches on theseveral stages of a transmitter can be ganged'tooperate simultaneously from a single control member.

The inherent inductanc'e'of the switch arms-is 7 made low so that very short wavelengths are obtainable. The large width in the axialdirection of the switch-arm loop, where the highfrequency current mainly flows, namely on the inside faces, permits a heavy current capacity switch jaw to be employed. The heating which,

has heretofore been experienced isthus minimised. The inductance coils can be'mounted on a vertical panel or on pillars so'that the group of coils-can bereadily housed in the transmitter cubicle whilst ready access to thecoils canbe provided by the provision of suitable doors in the cubicle. V V 7 If desired theseveral inductance's mounted on the panel or elsewhere may be shielded from one another. For this purpose metal plates extending between the inductances maybe secured to the panel.

According to-a subsidiary feature of themes.

tion the switch arms, instead'of being moved by manual operation may be movedbiy means of an electric motor such as under push button control,

limit switches being employed to stop the motor when the switch arms occupy an operative position.

The invention also includes the particular form of jaw contacts hereinafter described in detail.

The features of the present invention may be used in association with the features of our applications Serial No. 516,104 for Multirange tuner for ultra high frequency transmitters, Serial No. 516,108 for Multirange tuning means for a radio frequency generator, both filed December 29, 1943, and our Patent No. 2,420,657, granted May 20, 1947, for Tuner.

Certain considerations leading to the invention and certain arrangements thereof by way of example will now be described with reference to the accompanying drawings in which:

Figs. 1 and 2 are electrical diagrams illustrating preferred embodiments of the invention.

Figs. 3, 4 and 5 are similar diagrams illustrating the application of the basic features of the invention.

Fig. 6 is a view in elevation showing the invention applied to the anode and grid circuits of a particular form of valve, and

Fig. 7 is a plan view of the anode portion of Fig. 6 showing the invention applied to a pair of the valves in push-pull.

Figure 7A shows a modified arrangement of the Figure 7 structure.

Fig. 3 is a view in greater detail showing the preferred actual contact arrangement of the switch blade and co-operating jaw.

Fig. 9 is an electrical diagram showing a pushpull output and drive circuits of a radio transmitter to which the present invention, and those of the other applications of even date herewith aforesaid, may be applied.

Referring first to Figs. 1 to 5 of the accompanying drawings, it is assumed that the present invention is applied to a pair of push-pull valves in accordance with Fig. 1 of British Letters Patent No. 414,753 but turned upside-down and that the anodes are resonated with the screening grids which are effectively earthed so far as high frequency currents are concerned.

In the accompanying Figs. 1 and 3, I is the efiective earth, 2 are the screening grids and 3 are the anodes of the push-pull valve, and it will be appreciated that each screening grid 2 and associated anode 3 provides a capacity, namely the valve capacity by which for very low wavelengths the tuning of the anode circuit may be mainly effected in combination with the inductance t. In Fig. 1 there is shown a condenser 5 in parallel with the inductance 4 which condenser may be a trimming condenser or it may in fact be necessary for effecting exact tuning when the inductance coil 15 is changed for changing the wavelength of the transmission. As an example the anode to earth capacity may be of the order of 55 micromicrofarads and the anode swing may be 8,000 volts in the case of the parallel circuit shown in Fig. 1.

Fig. 2 indicates a series tuning circuit wherein 6 represents the screening grids and cathodes of the two valves, I being the effective earth as before, whilst I may represent the control grids of said valves. In this case there are two similar inductances i and la having the trimming or tuning condenser 5a in series between these inductances. In the system shown in Fig. 2 the grid to earth capacity may be 88 micromicrofarads and the grid swing may be 1500 volts.

If as in accordance with the present invention wave changing is efiected by switching diflerent inductance coils 4, or pairs of coils 4 and to into circuit by means of the switch arms, the latter will have finite inductances indicated at8 in Figs. 3, 4 and 5. Considering for the moment Fig. 3 it will have been appreciated that the inductances 8 of the switch arms should be made as small as is practicable and this is achieved by means of the present invention.

In some cases such as in the grid circuits when efiecting wave changing it may be desirable to change the connection of the condenser 511 from series connection (Fig. 4) to the parallel connection (Fig. 5) by means of the switch arms 8. For the parallel connection of the same or another condenser Ea (Fig. 5) in at least one position of the four switch arms they will engage two straight straps 9 with the freshly selected coil 4b permanently connected to them.

Referring next to Figs. 6 and 7 of the accom panying drawings and more especially Fig. 6, at It} is shown the anode of a valve which may be assumed to be an inverted form of the valve illustrated by Fig. 1 of British Letters Patent No. 414,753 (aforesaid). That valve, as diagrammatically shown, further comprises a coaxial insulating envelope portion I I, a screening grid terminal I2, another tubular insulating portion I3, a control grid terminal I4, a further insulating envelope portion I5 and a cathode terminal I6, whilst at I! is shown part of the earthed chamber containing the control grid circuits, all as described, with the exception of the actual circuits, in the prior Letters Patent just above mentioned. It is to be assumed furthermore, as indicated by Fig. 7, that there are two of such valves with their vertical axes parallel with each other.

Each anode I I] has secured to it or integral with it an anode terminal I8 carrying on a lug I9 a piv-- oted switch arm 20. The two switch arms 20 are adapted for simultaneous operation by means of a shaft 2I.

Each switch arm 20 is broad in the longitudinal direction, that is to say in the direction parallel with the efiective axis of the inductance loop comprised between the two arms 26 and the inductance, as best seen from Fig. 7. Each arm 2a is adapted to engage jaws 22, 23, 24 which are mounted upon brackets 25 secured on an insulating panel as indicated at 26 or on a pair of insulating pillars (not shown). The brackets 25 have terminals 21 on the right-hand side of the panel (or pillars) 26 and between each corresponding pair of terminals 21 is fastened an inductance 28 or 29 or 30. The values'of the three inductances (Fig. 6) are all different so that by the simultaneous movement of the pair of switch arms 2!) as between the jaws 22 or 23 or 24 the transmission wavelength may be varied. A nearly identical switching arrangement is provided for the grid circuit and in Fig. 6 the grid switching and inductance arrangement is assumed to be in general smaller but otherwise similar to the anode switching arrangement illustrated, and primed reference numerals are used to designate elements corresponding to those used in the anode switching arrangement.

' Hence, a description of the grid circuit is con- I'helical coils it will be appreciated that if shorter wavelengths are required these coils may be replaced by straight bars as hereinafter described in connection-with Figure 7A. These *bars may be :all of equal length but nevertheless the Irecluired variation in wavelength "is obtained by movement of the switch arms 2!! amongst the jaw contacts 22, 23 and '24, since as. explained in the above mentioned application .Serial No. 516,104,

the further -the inductance loop is removed from the --'effeotive ear;th to which the anodes are :rescoated, in this casetheelectrode 12 and .screening box ll, the greater is the value of the finductance.

Even with straight inductance bars as above mentioned it will be appreciated that the inductance loop is still relatively large since the switch arms 2 d must have reasonable length in relation to voltage -clearances and in addition the jaws 23 lorackets 2-5 also necessarily have length whereby the inductance value is increased. As explained in our application Serial No. 516,104 just above mentioned the shortest possible inductance loop is obtained when there is a straight bar directly connecting the anodes of the two valves.

According to another subsidiary feature of the present invention the inductance values when employing wave changing arrangements such as illustrated by Figs. -6 and 7 are still further reduced, as indicated in Fig. 7A, by securing straight bridges :on the brackets 25 and jaws 23 so as to be nearer the pivot of the switch arms to than are bars (not shown) secured :across the terminals 21..

Thus, in Fig. 7A 28a represents a transverse bar or bridge directly connecting together. the fixed jaw contacts :23. r

In Figs. 6 and '7 theswitcharms 2c are shown as simple :blades engaging between fixedvjaws which are rendered somewhat "more resilient by the provision of saw cuts Etherein. Since, however, the high frequency currents flow mainly on the inside -.of the inductance loop and since the undesirable heating through poor contact .may :occur on one side of the switch jaw and .arm, the particular switch arm and jaw illustrated-in Fig. 8 is preferred since it has been found 'to have greater :efiiciency f or highifrequency switching operations.

In Fig. 8, 18 may :be assumed to :be the anode or grid terminal of a valve and .19 the lug .integral therewith, the lug ipivotally carrying .a switch :arm comprising .a pair of blades 3! spaced at the pivotal end by :a separator .or :boss 2.

In the arrangement shown in Fig. .8 the switch jaw comprises a pair of blades .33 which are spaced apart and :may be directly clamped, .ior example .upon an insulating pillar 2.611. The blades '33 have secured :between'them a spacer 34; each blade '38 has its left-hand rend :bent

' inwards as shown at '35 and the .bent in portion is formed with a knife'edgeso :as to obtain substantially line contact with the outer faces of 7 comprising aspring :36 tending to ungetheblade's 34" apart, .a sheet-of thichmetal foil 31 soldered to said blades whereby to improve the high frequency characteristics of the switch arm: similarly :foil (not shown) :may be connected across the .fiXed bladesdii. .It will :be appreciated that alternatively the knife edges may be pro- ".vided arm .the switch blades 3| instead ofwon zthe According @to .a further feature of the invention illustrated by Fig. :8 the several jaws with'their :knife edges, which jaws co-operate with the single switch arm 3i, 3|, are arranged so that the knife edges of the several jaws mate with difierent pairs of lines :of the outer faces of the blades 3i This is achieved by disposing the knife edges of the different jaws :at slightly different distances from the axis of the shaft 2|". In this manner greater consistency of electrical contact is obtained than with any prior switch- .ing arrangement of a "generally far as applicants are aware.

Referring lastly :to Fig. 9 of the accompanying drawings, at .38 are shown the push-pull output valves, the anodes :of which are connected to the similar kind, so

switch arms 29 which can be moved so that any one :of the anodeinductances 2.8, 29 and 3]! can be connected in circuit; each inductance hasrconnected to it through :blccking condensers '39 the feeders :38 each of which may be con- :nected through a matching transformer 44 to a =di-po'le aerial 132. There :are thus three different aerials for .the different wavelengths required.

The tuning condenser or condensers for the anode induota'nccs are. omitted :to avoid .confusiion. At G3 are indicated the high-tension deads to the centre point 0f the inductances,

for providing the anode potential.

Thescreengrids id of the valves 38.:have assovcLa-ted with them the metal screening box 45 within which are threeequivalent grid circuit inductances and switch arm's-therefor. lit-45 are shown the grid feeder :leads passing from the screening loox 2&5, apreferablyas concentric condoctors in tubes dl, into the anode ..screening' box, part of which :is indicated at 58, of .the preceding stage which from the point of view of theacihcuit diagram. may :be identical with the output :stageillustrated .andjust above described. It may consist of amplifier or oscillator valves '53 with associated anode condenser .58, and coils 543 and chosen by the selector arm. The

output :is :shown as taken from the said anode coils tvia coupling condenser 53 and grid feeder leads 52 to the aforementioned grid jcircuitin- -ductances id, :59 and 35.4..

permanently connected by a feeder to each corresponding inductance coil of the output valves the blades 31 of theswitchzarm. The arrange V *men tshown in Eig.i8 includes :rurther refinements whereby fecdor switching is avoided to considerable advantagc. I

r ilrerembetore iset. rorth all the inductance selector switches of any particular transmitter, such as all those shown in Fig. 9, and switches of any earlier stages, not shown, may be operated simultaneously, preferably by motive power. Furthermore, according to a subsidiary feature of the present invention the switch changing operations are efiected by means of push-button control, all the shafts of the several groups of switch arms being coupled together for simultaneous and similar actuation such as by levers and links, sprocket chains, gear wheels or the equivalent, whilst limit switches are provided which ensure that the rotating switch arm shafts are caused to come to rest when the arms are properly mated with their selected switch jaws or other fixed inductance contacts. No description is given of such a control since it can be readily devised by anyone skilled in the art of industrial or other electric machine or apparatus control. However, reference may be had to the mechanical arrangement or layout, for an output stage for example, including limit switches and also automatic condenser adjustment, as illustrated and described in the above-mentioned Patent No. 2,420,657.

We claim:

1. A radio transmitter of the character described, including a pair of push-pull valves, a movable contact element, a plurality of different inductances arranged in fixed relation to the valves, a fixed contact element connected to the terminals of each of said inductances and adapted to be engaged by said movable contact element, said movable contact element being connected, by electrically integral connections, with the valve electrode terminals to which the several inductances are required to be selectively connected, said connections and contact elements having relatively large dimensions in the direction parallel with the axes of the inductance loops formed by said connections and contact elements.

2. A radio transmitter of the character defined in claim 1 wherein a single condenser is provided for the several inductance coils.

3. A radio transmitter of the character defined in claim 1 wherein said movable contact element comprises spaced arms, a condenser for the inductances, and means to connect the condenser selectively to the inductances, said means including switch arms positioned between the inductance selecting movable contact arms and operable simultaneously with the latter.

4. A radio transmitter of the character defined in claim 1 wherein a single condenser is provided for the several inductances, movable switch arms to selectively connect the inductances with said condenser to place the latter in parallel with one of the inductances and in series with another of the inductances.

5. A radio transmitter of the character defined in claim 1 including means to connect a feeder between each of the inductances in .one stage and the corresponding inductance of the group in another stage;

6. A radio transmitter of the character defined in claim 1 wherein means is provided to connect said inductances to anodes of the valves, and means to permanently connect each anode by its own feeder to one of a number of aerials.

7. A radio transmitter of the character defined in claim 1 wherein each fixed contact element comprises a pair of spaced arms, and a bridge inductance extends between said arms to reduce the resonance wave length.

8. A radio transmitter of the character defined in claim 1 wherein the movable contact element comprises a pair of spaced arms, and a bridge inductance extends between said arms to reduce the resonance wave length.

9. A radio transmitter of the character defined in claim 1 wherein said movable contact element is pivoted.

10. A radio transmitter of the character defined in claim 1 wherein said movable contact element is pivoted to the valve terminals.

11. A radio transmitter of the character defined in claim 1 wherein said movable contact element is pivotally mounted and one of said contact elements is provided with a knife edge to engage the other contact element.

12. A radio transmitter of the character defined in claim 1 wherein said movable contact element is pivotally mounted, each of said elements comprises spaced arms, one of said contact elements is provided with a knife edge to engage the other contact element, and the arms of at least one element have metal foil connected across them.

13. A radio transmitter of the character defined in claim 1 wherein each fixed contact element is provided with a knife edge, the movable contact element is pivoted, and the knife edge on each fixed element is positioned at difierent distances with respect to the pivot of the movable contact element.

JOHN MATHIESON DODDS. JOHN HEYWOOD LUDLOW.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number 

